Elidibus would be pleased to discover if things like Esuna and Dispel can help some folk out of their mind-fog. He would absolutely help Tidus find targets to approach (You are absolutely welcome to handwave this if it helps as a hook for CR!) Specifically Elidibus would be able to help pinpoint people who were wearing their SCAs at the time of the mission start. He also has the roster memorized, though he hasn't met a lot of people face to face.

Elidibus would also give Tidus a rundown of places that are 'hotspots' or high risk for falling back under the illusion's sway. (and you can safely say that the info Elidibus learns Tidus can have had explained to him). He would, however, be hesitant to encourage people to charge at the entity, though he is willing to admit that he has not had the same experiences others have.

Our friendly resident Ascian would however, be more inclined to guide Tidus toward freeing people and keeping them safe while they find a way out of the illusion, back to the train and/or a safe place for all the captive people. Who aren't illusions. Especially as things start to crumble apart.

(Elidibus will absolutely appreciate Tidus' physical backup when nightmare monsters and crumbling city days come into effect.)